Each year over a million patients worldwide undergo cardiac surgery requiring cardiopulmonary bypass (CPB). CPB is associated with significant morbidity including the transfusion of allogenic blood products, inflammation and hemodynamic instability. In fact, approximately 20% of all blood products transfused are associated with coronary artery bypass grafting procedures. Transfusion of allogenic blood products is associated with well-documented morbidity and increased mortality after cardiac surgery. Enhanced fibrinolysis contributes to increased blood product transfusion in the perioperative period. CPB activates the kallikrein-kinin system (KKS), leading to increased bradykinin concentrations. Bradykinin, acting through its B2 receptor, stimulates the release of nitric oxide, inflammatory cytokines and tissue-type plasminogen activator (t-PA). Based on data indicating that angiotensin-converting enzyme (ACE) inhibitors reduce mortality in patients with coronary artery disease, many patients undergoing CPB are taking ACE inhibitors. While interruption of the renin-angiotensin system (RAS) reduces inflammation in response to CPB, ACE inhibitors also potentiate the effects of bradykinin. The current proposal derives from data from our laboratory and others elucidating the role of the KKS in the inflammatory, hypotensive and fibrinolytic response to CPB. Specifically, we have found that CPB activates the KKS and that ACE inhibition and smoking further increases bradykinin concentrations. During CPB, bradykinin concentrations correlate inversely with mean arterial pressure and directly with t-PA. Moreover, we have found that bradykinin receptor antagonism attenuates protamine-related hypotension following CPB. The current proposal tests the central hypothesis that endogenous bradykinin contributes to the hemodynamic, fibrinolytic and inflammatory response to CPB and that bradykinin receptor antagonism will reduce hypotension, inflammation and transfusion requirements. In SPECIFIC AIM 1 we will test the hypothesis that the fibrinolytic and inflammatory response to CPB differ during ACE inhibition and angiotensin II type 1 receptor antagonism. In SPECIFIC AIM 2 we will test the hypothesis that bradykinin B2 receptor antagonism attenuates the hemodynamic, fibrinolytic, and inflammatory response to CPB. In SPECIFIC AIM 3 we will test the hypothesis that bradykinin B2 receptor antagonism reduces the risk of allogenic blood product transfusion in patients undergoing CPB. These studies promise to provide important information regarding the effects of drugs that interrupt the RAS and generate new strategies to reduce morbidity in patients undergoing CPB.